a(n) = 6^n - 5^n.

Terms

a(0) =0a(1) =1a(2) =11a(3) =91a(4) =671a(5) =4651a(6) =31031a(7) =201811a(8) =1288991a(9) =8124571a(10) =50700551a(11) =313968931a(12) =1932641711a(13) =11839990891a(14) =72260648471a(15) =439667406451